TNT Motorsports
TNT Motorsports

Backspacing & Offsets

Are you interested in buying a new set of wheels for your ride?  You know the style of the wheel, and the diameter, but will the wheels  fit? While the diameter of a wheel fires the imagination-you just gotta have 24s  filling the wheel wells, right?-the backspace or offset of a wheel are necessary  for determining how a wheel will fit inside of your fender. Most wheels' product  descriptions include backspace and/or the offset, along with width and diameter.  But, what is backspace and its cousin, offset, all about?

Here's an explanation of what backspace and offset mean. Backspace is the  distance from a wheel's mounting surface to the back edge of the wheel in  inches. By "back" we mean the brake side of the wheel. Offset measures the  distance from the mounting surface of the wheel to the centerline of the wheel,  and it is often indicated in millimeters. If the mounting surface is located  closer to the street side of a wheel, then the offset is positive. If it is  located closer to the brake side of wheel, then the offset is negative. If it is  in line with the center of the wheel, then the offset is zero.



An example may simplify this: The centerline of a 10-inch-wide wheel is at  five inches. If the wheel has a 6-inch backspace, then the offset is positive.  Conversely, a 4-inch backspace would make the offset negative. A wheel that has  a positive offset-or greater backspace-has to slide further into the wheel well  to be mounted. Similarly, one with a negative offset-or lesser backspace-will  tend to jut closer, or even beyond the fenders. By the way, spacers can be used  to change the offset, as well. They slide over the wheel studs, sandwiching  between the wheel and hub, creating negative offset, in a way, and thereby  widening the track of the vehicle. Off-roaders often use this approach.



If you want to slam your suspension and tuck your tires,  then it makes sense that you would lean toward a wheel with a positive offset  (more backspace). But a negative offset (less backspace) might give you the room  you need for that lifted look with big, knobby tires. There are other  considerations, as well. If you have too little backspace, then a wheel is more  likely to rub the brakes-or the suspension components. However, too much  backspace and your tires may rub the fenders.


As you can see, backspace and offset are closely related. As we said before,  many manufacturers have done the work for you by using both measurements in  their product descriptions. Want to know how to calculate them on your own? Our  sidebars will show you how to do just that.



Quick Equations
Here are some crib notes for figuring out  backspace, centerline, and offset.


* Step 1: Measure the room in  your wheel wells relative to the wheel hub.
* Step 2: Backspace = The distance from back of the wheel to the wheel's mounting space,  in inches.
* Step 3: Centerline = The wheel width divided by  2, in inches.
* Step 4: Offset = Backspace - Centerline,  which will be positive or negative, in inches.
* Step 5: Offset in Millimeters = Offset x 25.4.]


What Is My Wheel's Backspace?  To determine the wheel's  backspace, lay the wheel flat on the ground with the back facing upward. Next,  lay a straightedge across the wheel and measure the distance from the back of  the mounting surface to the strait edge. The backspace of the wheel pictured  here is 5.25 inches. We calculated the wheel's offset in the quick equations. 


What is My Truck's Backspace?   You can measure how much space  your truck has for wheels by making all your suspension, brake, and fender mods first.  Then, simply measure the distance from the wheel hub on the spindle/axle back  toward the first obstruction, such as your tie rods, etc. This will give you an  idea of how much wheel backspace your truck can handle. Measure from the hub to  the fender to find the amount of front space you can handle there, too. Next, we  will calculate a wheel's backspace.


What Is My Wheel's Offset?  To find the offset, start by  determining the wheels' centerline. To obtain that, first measure the wheel's  overall width from one outside edge to the other. Do note, that's not  necessarily the same as the width given in the manufacturer specs. For example,  the width in 20x8.5 inches refers to the distance between the inner flange and  outer flange. Next, divide the width in inches by 2 to find the centerline. The  width of this wheel is 9.5 inches, so its centerline is at 4.75 inches. Then,  subtract the centerline value from the backspace value to find your offset in  inches (5.25-4.75=.5). If the resulting number is negative, then your offset is  negative, and the opposite goes for a positive offset. If the centerline value  and backspace are the same, then the offset is zero. Don't forget, this number  is still in inches. To convert, multiply it by 25.4 to get the offset in  millimeters. The offset of this wheel is +.5 inch or +12.2 mm. Our result is a  few millimeters from the manufacturer's listed offset. We tried to illustrate  the offset in the photo that shows the two lines drawn on a straightedge, which  indicates the position of the wheel's mounting surface to its centerline. We  recap the equations we used to get backspace and offset in the following quick  equations.

What Do Positive and Negative Look Like?   Negative offset  configurations are often found on lifted trucks and look badass. On the other  hand, negative offset on a lowered truck can look just plain bad. Take a look at  these three trucks. A lifted one's offset can make the wheels stick out-in order  to clear those big tires.


Where to Find Us:

TNT Motorsports
13123 E 11th St
Tulsa, OK 74108


Phone: (918) 845-1935

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